Hurricane Irene and Global Warming: A Glimpse of the Future?

Nowadays, whenever there’s an Irene-like event—a huge storm, a terrible flood, a killer heat wave—the question is raised: was this caused by global warming? The very frequency with which this question is being asked these days should make people take notice, but the answer that comes back is usually squishy enough to allow them to forget about the issue until the next disaster occurs, at which point the process starts all over again. The problem here, as several commentators have pointed out this weekend, is that the question being posed is not the question we should be asking.

The standard answer to the question “Was Irene (or the recent flooding along the Missouri River, or the current record-breaking Texas drought, or [choose your own favorite example]) caused by global warming?” is: No one event can be definitively attributed to climate change (though in some cases, you can get pretty close). Hurricanes fall into the category of “weather,” which is driven partly by large and predictable forces and partly by those that are stochastic, or random.

How about posing the question this way: Are more events like Irene what you would expect in a warming world? Here the answer is a straightforward “yes.” In fact, experts have been warning for years that New York will become increasingly vulnerable to storm surges and flooding as the planet heats up. In 2009, the New York City Panel on Climate Change, appointed by Mayor Bloomberg, concluded that, as a result of global warming, “more frequent and enhanced coastal flooding” was “very likely” and that “shortened 100-year flood recurrence period” was also “very likely.” Much of the problem simply has to do with sea levels—as these rise, any storm or storm surge becomes more dangerous. Marcus Bowman, an oceanography professor at Stony Brook University, has warned that the city could one day have “flood days,” the way it now has snow days.

Meanwhile, rising temperatures make other risks worse as well. Warm air holds more moisture, so as temperatures rise there is more water available to the system. And warmer ocean temperatures mean there is more energy available to fuel severe storms like Irene. As Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research, in Boulder, explained recently on the blog Climate Progress, “Owing to higher SSTs [sea surface temperatures] from human activities, the increased water vapor in the atmosphere leads to 5 to 10% more rainfall and increases the risk of flooding.” Also, “because water vapor and higher ocean temperatures help fuel the storm, it is likely to be more intense and bigger as well.”

When we add all of these risk factors together, we can say with a great deal of confidence that in the future, there will be more and more events like Irene. We can comfort ourselves by saying that this particular storm was not necessarily caused by global warming. Or we can acknowledge the truth, which is that we are making the world a more dangerous place and, what’s more, that we know it.